The present invention relates to counterfeit detectors for United States paper currency. With modern improvements in copying methods it has become relatively easy for counterfeiters to reproduce paper currency. The production of passable copies no longer requires the work of a skilled engraver. Photographic methods can be used to make accurate plates in a very short time. In addition electrostatic copying equipment has been so perfected that reasonable color copies of legitimate notes can be made easily and rapidly. As a result there has been a steadily growing amount of false currency and an increased cost to merchants and others who must absorb the loss when these copies are passed.
Some methods to detect counterfeit employ special illumination. Because United States bills are printed on rag bond and use no brighteners, they possess characteristic optical properties. Under ordinary light they will have an off-white appearance. Under ultraviolet illumination they will not fluoresce. Papers containing wood pulp and brighteners will not have these properties. A new paper has become available to some counterfeiters however which more closely resembles that used for legitimate notes.
Despite the use of optical machines the most effective detection of counterfeit to date has been by highly trained observers who look for small imperfections in the printing. It is an object of this invention to provide a simple apparatus whereby persons of limited training will be able to check suspected paper currency. It is another object of this invention to force would-be counterfeiters to meet new standards in addition those involved with paper quality and printing accuracy, thereby increasing the difficulty of producing passable imitations.